1. Field of the Invention
This invention relates to a vehicle seat, which comprises a seat pad, a trim cover and a planar member, such a heater mat or a sensor mat, located between the seat pad and the trim cover.
2. Description of the Related Art
Vehicle seats are known, each having a planar member such as a heater mat or a sensor mat. The planar member is on a seat cushion or a seat back, or on both, located between a seat pad (cushion member) made of foamed material such as foamed urethane, and a trim cover (surface layer) covering the seat pad.
Most seat pads have grooves (i.e., pulling-over grooves) each, which are cut in the upper surface. The grooves have an almost rectangular cross section, and extend in the front-to-aft direction and left-to-right direction of the vehicle. Below one of the grooves, a suspension wire is embedded in the seat pad, and the planar member has slits cut in alignment with said groove of the seat pad. A suspender is sewn to the trim cover, hangs down to the groove through the slits and is coupled to the suspension wire. The suspender is pulled, pulling that part of the trim cover, which is sewn to it, into the groove. So pulled and stretched, the trim cover assumes a desirable outer appearance (Refer to, for example, JP 2004-350827A).
The sewn part of the trim cover is pulled into the grooves of the seat pad, that part (i.e., bridge part of the planar member, which has no slits and extent over the grooves), is pushed to the sewn part of the trim cover. As a result, said part of the planar member is pulled into the groove, together with the sewn part of the trim cover, is bent and shaped like letter U, and is held in the grooves.
As a person gets seated, a load is applied to the seat. The seat pad is therefore bent, undergoing compressive deformation. As the seat pad undergoes compressive deformation, the trim cover expands. However, the planar member, which is composed of a flexible film embedding a heater wire, a sensor mat wire, etc., is poor in elasticity. Inevitably, the bridge part of the planar member is pushed downwards onto the bottom of the groove made in the seat pad, and the seat pad undergoes compressive deformation. So pushed, the bridge part warps and may be broken. If this happens, the heater wire and the sensor mat wire may be cut at the bridge part.
JP 2003-291708A discloses a configuration, in which cut pieces made of polyethylene terephthalate (PET) and therefore thin and able to slide and having elastic force, are bonded to the bridge part of the planar member. The cut pieces therefore render the planar member thicker, enable the planar member to slide more readily, and imparts a larger elastic force to the planar member. In this configuration, the seat pad receives a load and undergoes compressive deformation as a person gets seated. Then, the planar member slides outwards and upwards from the grooves, and warps at its greater part. Therefore, the planar member is pulled less into the grooves, preventing the bridge part from being pushed onto the bottoms of the grooves and, hence, from being broken.
JP 2012-034719A describes a bridge part held in groove, in the form of U, while clamped with a fastening member fitted in the groove. The bridge part is therefore prevented from being pushed onto the bottom of the groove and, hence, from being broken.
In the configuration disclosed in JP 2003-291708A, the cut pieces are bonded to the bridge part of the planar member. Inevitably, the number of components increases, and an additional step of bonding the cut pieces to the bridge part must be performed. Further, the planar member slides above the groove and outward from the grooves, and a greater part of the planar member warps and is pulled into the grooves but insufficiently. Unless the planar member sufficiently slides to warp at its greater part, its bridge part cannot be prevented from being pushed onto the bottoms of the grooves or from being ultimately broken. Consequently, the heater wire will probably be broken.
In the configuration disclosed in JP 2012-034719A, the bridge part of the planar member is secured by fastening members fitted in the grooves. Therefore, the bridge part is not pushed onto the bottoms of the grooves. However, any part of the bridge part, which is not so secured, may be bent and broken. Further, the number of components increases (due to the use of the fastening members). Still further, an additional step of holding the bridge part with the fastening members must be performed, inevitably rendering the manufacture procedure more complex.